Rho-associated protein kinase (ROCK) is a key intracellular regulator of cytoskeletal dynamics and cell motility. Rho-kinase regulates a number of downstream targets of RhoA through phosphorylation, including, for example, myosin light chain, the myosin light chain phosphatase binding subunit and LIM-kinase 2. These substrates regulate actin filament organization and contractility. In smooth muscle cells Rho-kinase mediates calcium sensitization and smooth muscle contraction. Inhibition of Rho-kinase blocks 5-HT and phenylephrine agonist induced muscle contraction. When introduced into non-smooth muscle cells, Rho kinase induces stress fiber formation and is required for the cellular transformation mediated by RhoA. Rho kinase participates in a variety of cellular processes, including but not limited to cell adhesion, cell motility and migration, growth control, cell contraction, and cytokinesis. Rho kinase is also involved in Na/H exchange transport system activation, stress fiber formation, adducin activation, and physiological processes such as vasoconstriction, bronchial smooth muscle constriction, vascular smooth muscle and endothelial cell proliferation, platelet aggregation, and others.
Inhibition of Rho-kinase activity in animal models has demonstrated a number of benefits of Rho-kinase inhibition for the treatment of human diseases. These include models of cardiovascular diseases such as hypertension, atherosclerosis, restenosis, cardiac hypertrophy, ocular hypertension, cerebral ischemia, cerebral vasospasm, penile erectile dysfunction, central nervous system disorders such as neuronal degeneration and spinal cord injury, and in neoplasias. Inhibition of Rho-kinase activity has been shown to inhibit tumor cell growth and metastasis, angiogenesis, arterial thrombotic disorders such as platelet aggregation and leukocyte aggregation, asthma, regulation of intraoccular pressure, and bone resorption. The inhibition of Rho-kinase activity in patients has benefits for controlling cerebral vasospasms and ischemia following subarachnoid hemorrhage, reduction of intraocular pressure, increase in ocular aqueous outflow by relaxation of trabecular meshwork tissue, improving blood flow to the optic nerve, and protection of healthy ganglion cells.
In mammals, Rho-kinase consists of two isoforms, ROCK1 (ROCKβ; p160-ROCK) and ROCK2 (ROCKα). ROCK1 and ROCK2 are differentially expressed and regulated in specific tissues. For example, ROCK1 is ubiquitously expressed at relatively high levels, whereas ROCK2 is preferentially expressed in cardiac and brain and skeletal muscle. The isoforms are also expressed in some tissues and in a developmental stage specific manner. ROCK1 is a substrate for cleavage by caspase-3 during apoptosis, whereas ROCK2 is not. Smooth muscle specific basic calponin is phosphorylated only by ROCK2.
Given the extent of involved cellular processes and diseases, compounds that selectively inhibit one rho kinase, or inhibit ROCK1 and ROCK2, are desired.